This invention relates to a media detector for use in an automatic teller machine, vending machine, scanner, copier, or other machine that must handle money, paper, plastic cards, or similar flat media.
Such a machine typically has a pair of flat media guides separated by a small gap forming a path through which media are transported by rollers. To monitor the passage of media on this transport path, the machine has a media detector comprising, for example, a light-emitting diode mounted above the upper media guide and a photodiode mounted below the lower media guide. The optic axes of these diodes are aligned with each other and with holes in the media guides so that normally a beam of light emitted by the light-emitting diode illuminates the photodiode. The presence of media in the path is detected when this beam is interrupted. If necessary, a row of two or more such pairs of diodes can be positioned across the transport path to detect the size, shape, or orientation of the media. The diodes are connected via cables to amplifier and detector circuitry on a separate printed circuit board.
A problem with this scheme is that additional structure is needed to support the diodes above and below the media guides. This structure, and the above-mentioned interconnecting cables, tend to get in the way during maintenance. The cables, moreover require connectors, which take up space and pose a reliability problem in that the cables may become accidentally loosened or detached. Furthermore, the complexity of the mounting and cabling adds to the cost of the detector. When more than one pair of diodes is employed, all these problems are multiplied.